1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a differential amplifier, a method for amplifying signals of the differential amplifier, and a display driving device having the differential amplifier.
2. Description of Related Art
A display driving device, which is referred to as a source driver or a data line driver, is used to drive a flat panel display device, such as a liquid crystal display (LCD). FIG. 1 is a circuit diagram showing an output portion of a general display driving device. Referring to FIG. 1, an output portion 10 of a display driving device includes a digital-to-analog converter (DAC) 11, a plurality of buffers 13-1, 13-2, 13-3, . . . , 13-n, where “n” is a natural number, a bias voltage generator 15, a plurality of first transmission switches 17-1, 17-2, 17-3, . . . , 17-n, and a plurality of second transmission switches 19-1, 19-2, 19-3, . . . , 19-n. The DAC 11 converts input digital image data DATA to analog signals inp1, inp2, inp3, . . . , inpn.
Each of the buffers 13-1, 13-2, 13-3, . . . , 13-n receives and amplifies a corresponding one of the analog signals inp1, inp2, inp3, . . . , inpn output from the DAC 11. Each of the buffers 13-1, 13-2, 13-3, . . . , 13-n can be embodied by an operational amplifier, for example, a rail-to-rail differential operational amplifier or a unit gain buffer, each of which is known in the art.
The bias voltage generator 15 supplies bias control voltages to each of the buffers 13-1, 13-2, 13-3, . . . , 13-n so that each buffer can normally perform an amplification operation. During the amplification operation, for example, when a control signal SW has a high level and a complementary control signal SWB has a low level, each of the first transmission switches 17-1, 17-2, 17-3, . . . , 17-n, in response to the control signals SW and SWB, supplies a voltage amplified by each of the buffers 13-1, 13-2, 13-3, . . . , 13-n to each of a plurality of data lines Y1, Y2, Y3, . . . , Yn. Each of the second transmission switches 19-1, 19-2, 19-3, . . . , 19-n maintains an off state in response to a plurality of charge sharing control signals CS_SW and CS_SWB.
During the charge sharing operation, for example, when the charge sharing control signal CS_SW has a high level and the complementary charge sharing control signal CS_SWB has a low level, each of the second transmission switches 19-1, 19-2, 19-3, . . . , 19-n is connected to a corresponding one of the plurality of data lines Y1, Y2, Y3, . . . , Yn, in response to the charge sharing control signals CS_SW and CS_SWB. Each of the first transmission switches 17-1, 17-2, 17-3, . . . , 17-n maintains an off state in response to the control signals SW and SWB.
Since each of the buffers 13-1, 13-2, 13-3, . . . , 13-n includes an operational amplifier consuming a large amount of power, most of the power consumed by the display driving device is consumed at the output portion 10. Thus, a display driving device having an improved structure that can reduce power dissipation generated in the output portion 10 is needed. Also, a buffer having an improved structure is needed.
Furthermore, since the display driving device includes the first transmission switches 17-1, 17-2, 17-3, . . . , 17-n, a layout area of the display driving device increases. Thus, as the number of data lines that the display driving device drives increases, the number of the first transmission switches 17-1, 17-2, 17-3, . . . , 17-n increases. Thus, a display driving device having an improved structure that reduces the layout area is needed.